A fault-tolerant computer system is generally composed of specially designed hardware and software components having improved tolerance to faults that enable their continuous operation. One of these components includes a system clock unit that generates and distributes clock signals to logic circuits located throughout the system. Preferably, the system clock unit generates clock pulses having fast cycle times that increase system performance by synchronizing high-speed operations of the logic circuits. However, continuous computer operation requires constant generation and transmission of these fast pulses by the system clock which, in turn, consumes significant amounts of power.
Many applications of the fault-tolerant computer do not require such high availability during non-working hours, such as weekends. For these applications, it may be desirable to conserve energy and reduce costs by periodically disabling the system clock. Yet, there is a requirement to maintain operation of selected computer components so that information relating to the "state" of the system can be accessed despite the absence of system clock signals. This information may be stored in memory devices resident on a remote connector interface component of the fault-tolerant system that is sequenced by a low-power, local clock unit. The present invention is concerned with switching between the system and local clock units in a manner that provides a continuous stream of clock signals to circuits of the computer system and, thus, uninterrupted operation of these selected components.